The present invention relates to an installation for the continuous cleaning of a wiping roller of a machine for direct plate or copper-plate printing in one or more coulours, comprising a container for receiving the cleaning liquid which acts permanently on the wiping roller and cleaning members in contact with the periphery of the wiping roller comprising, in the direction of rotation of this roller, a first scraper constituting the first cleaning member, followed at fixed distances by several other members constituted by brushes and/or scrapers.
An installation is already known in which the wiping roller is immersed in the cleaning liquid contained in a reservoir, this installation comprising a first scraper forming an acute angle with the peripheral segment of the wiping roller and after this first scraper, in the direction of rotation of the wiping roller, several other scrapers and at least one fixed brush which are located in the humidification zone.
This installation which makes it possible to use an alkaline aqueous solution as the cleaning liquid, gives good results as regards the cleaning efficiency of the wiping roller, however, this design always requires an interruption of the operation of the installation for renewing the solution of the cleaning bath.
Hitherto, it has always been considered useful and necessary that the wiping roller is partly immersed in the cleaning bath. It was therefore very important that the cleaning bath be renewed completely as soon as it was full of small particles of ink in suspension, in order to eliminate the danger of these particles of ink being re-deposited on the surface of the roller. This required frequent interruptions in the operation of the installation.
Even if, with this type of known installation, it was envisaged to re-generate the solution by a closed circuit system, a time always comes, or after a certain operating time, the solution becomes dirty, spent and it is therefore necessary to stop the operation of the installation in order to empty the reservoir and clean its walls. This momentary stoppage of operation of the installation is always troublesome, since it reduces production, thus wasting a considerable amount of time.
The fact of using such a bath of cleaning liquid which becomes dirty slowly, has the drawback that the quality of printing generally undergoes a certain fluctuation in the course of an operating cycle of the installation, this quality of printing becomes worse and worse as the solution becomes dirty and, even by stopping the operation of the installation in order to renew the bath, it is not possible to avoid the fact that the quality of printing, which is excellent when the cleaning liquid has been renewed, gradually deteriorates. This fluctuation in the quality of printing is inadmissible when printing paper currency, in particular bank notes and in order to reduce this fluctuation in the quality to a maximum, it is necessary to interrupt the operation of the machine very frequently, in order to renew the solution.
With rotary printing machines having a high rotary speed, which are used at the present time, it may be necessary to interrupt operation of the machine every hour for approximately 15 minutes in order to renew the bath.
In fact, it is very important that this replacement of the used solution is carried out in good time, before any stain is produced on the wiping roller and is transferred to the sheet to be printed.